Novel multi-purpose bioreduction system for the large-scale production of chiral alcohols

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Chiral alcohols are useful intermediates for many kinds of pharmaceuticals and chemicals. Enzymatic asymmetric reduction of prochiral carbonyl compounds is a promising method for producing chiral alcohols. There have been many attempts to construct bioreduction systems for the industrial production of chiral alcohols. This study focuses on establishment of a novel bioreduction system using an E. coli transformant co-expressing carbonyl reductase and cofactor regeneration enzyme genes. This bioreduction system is applicable to the production of many other useful chiral alcohols, by replacing the carbonyl reductase gene with other appropriate enzyme genes for carbonyl reduction. A good library of carbonyl reduction enzymes with different substrate specificities and stereospecificities has been made. Therefore, this bioreduction system could be useful as a multi-purpose catalyst for the asymmetric reduction reactions.In addition to the carbonyl reductase reactions, this co-expression system might be applicable to the reactions requiring NAD(P)H as a cofactor, such as C=C bond reductions, reductive amination and so on. Old yellow enzyme from C. macedoniensis or S. cerevisiae was found to catalyze the asymmetric hydrogenation of C=C bond of enone compounds.The direct evolution technique, such as site-directed mutagenesis, random mutagenesis, and DNA shuffling, is an effective method for improvement or expansion of carbonyl reductase functions. Furthermore, public databases of genes encoding NAD(P)H-dependent carbonyl reductases (i.e., oxidoreductases or hypothetical oxidoreductases), determined by genome projects and so on, might also be good sources for expansion of the carbonyl reductase library. These trials might be more useful and effective in combination with traditional screening of enzymes.